JP2024051818A - Exhaust system for internal combustion engine, internal combustion engine and saddle-type vehicle - Google Patents

Abstract

[Problem] To provide a configuration that can contribute to the installation of an EGR system in a saddle-type vehicle. [Solution] An exhaust device 50 for an internal combustion engine 20 according to one embodiment includes an exhaust pipe 51c having an exhaust passage portion 66a through which exhaust gas discharged from a combustion chamber flows, and an EGR passage portion 68a. The exhaust pipe 51c has a partition wall 71 that separates the exhaust passage portion 66a and the EGR passage portion 68a. [Selected Figure] Figure 12

Description

The present invention relates to an exhaust system for an internal combustion engine equipped with an EGR passage portion, an internal combustion engine equipped with the same, and a straddle-type vehicle equipped with the internal combustion engine.

Efforts aimed at mitigating or reducing the impact of climate change have been ongoing for some time now, and research and development into emissions improvement is being conducted to achieve this. Specifically, it is known that exhaust gas recirculation (EGR) in internal combustion engines, which returns a portion of the exhaust gas back to the combustion chamber, can suppress the emission of harmful substances such as nitrogen oxides (NOx) and improve fuel efficiency, and this method has been widely put to practical use. There is a so-called external EGR method in which a portion of the exhaust gas flowing through the exhaust passage is returned to the intake passage via the EGR passage and sent to the combustion chamber. External EGR is put to practical use, for example, in four-wheeled automobiles, and generally comprises an EGR passage connecting the exhaust passage and the intake passage, an EGR valve provided in the EGR passage, and an EGR cooler provided in the EGR passage.

For example, Patent Document 1 discloses an exhaust gas recirculation device that supplies recirculated exhaust gas taken from downstream of a catalytic converter downstream of an exhaust manifold in an exhaust passage of a cross-flow multi-cylinder engine that takes in air from one side in a direction perpendicular to the cylinder row and exhausts from the other side to the intake passage via a water-cooled recirculation exhaust cooler and an exhaust gas recirculation control valve. According to the description in Patent Document 1, this engine is a transverse-type engine in which the cylinder row direction is approximately the vehicle width direction in the engine room at the front of the vehicle.

JP 2005-98171 A

However, the EGR device in Patent Document 1 is mounted on a four-wheeled automobile and is not intended for application to saddle-type vehicles such as motorcycles. EGR is also effective in improving emissions in saddle-type vehicles, but it is difficult to directly apply the EGR system in Patent Document 1 to saddle-type vehicles, for example, in terms of the installation space required for an EGR system to perform external EGR.

To solve the above problems, the present application aims to provide a configuration that can contribute to the installation of an EGR system in a saddle-type vehicle. This will ultimately contribute to mitigating or reducing the impact of climate change.

One aspect of the present invention is
an exhaust passage portion through which exhaust gas discharged from the combustion chamber flows;
an exhaust pipe having an EGR passage portion;
The exhaust pipe has a partition wall that separates the exhaust passage portion and the EGR passage portion.
The present invention provides an exhaust system for an internal combustion engine.

According to the above configuration, since the exhaust pipe has a partition wall separating the exhaust passage portion and the EGR passage portion, the EGR passage portion can be arranged adjacent to the exhaust passage portion in the exhaust pipe, and therefore the exhaust passage portion and the EGR passage portion can be integrated in the exhaust pipe, which reduces dead space and contributes to a more compact EGR system. Therefore, it can contribute to the installation of an EGR system in a saddle-type vehicle. In addition, since the exhaust pipe is configured with a partition wall separating the exhaust passage portion and the EGR passage portion, the appearance of the exhaust pipe can be made closer to or substantially the same as that of a conventional exhaust pipe, for example, compared to a case in which an exhaust pipe forming the aforementioned exhaust passage portion and an EGR pipe forming the aforementioned EGR passage portion are provided.

Preferably, the partition is provided in the exhaust pipe so as to define the EGR passage portion outside the exhaust passage portion. With this configuration, the exhaust pipe can be made to have, for example, a double pipe structure, and the EGR passage portion adjacent to the exhaust passage portion can be effectively formed while ensuring a sufficient cross-sectional area of the exhaust passage portion. In addition, an exhaust pipe with a double pipe structure can be manufactured at a relatively low cost, and this configuration is also excellent in terms of cost.

Preferably, the exhaust pipe is provided with a catalyst in the exhaust passage portion. With this configuration, the catalyst can be warmed up by exhaust gas flowing through the EGR passage portion. Also, in this configuration, when the EGR passage portion passes exhaust gas from the downstream side of the catalyst, the exhaust gas purified by the catalyst can be passed into the intake system of the internal combustion engine.

The present invention also resides in an internal combustion engine equipped with the exhaust device for the internal combustion engine. Preferably, the internal combustion engine further includes an EGR pipe section that defines a second EGR passage section that is connected to the EGR passage section of the exhaust pipe and extends toward the engine body. This configuration makes it possible to arrange the EGR pipe section compactly around the engine body, which can contribute to making the EGR system more compact, for example.

Preferably, the EGR pipe section is connected to the engine body. With this configuration, a portion of the EGR passage can be partitioned and formed inside the engine body, making it possible to further compact the EGR system. Alternatively, the EGR pipe section may pass around the periphery of the engine body and be connected to the intake pipe. This allows the EGR pipe section to be compactly arranged around the engine body, making it possible to design a compact EGR system.

Preferably, the EGR pipe section includes a heat dissipation section. With this configuration, the exhaust gas flowing through the EGR pipe section, i.e., the EGR gas, can be cooled more effectively.

Preferably, the internal combustion engine includes an air-cooled fan provided at one end of the crankshaft and an air guide member that guides the air from the air-cooled fan to the exhaust port of the engine body, and the EGR pipe section is arranged next to the exhaust port of the engine body so that it can receive the air discharged from the air guide member. With this configuration, the EGR pipe section, and in particular the exhaust gas flowing inside it, can be more effectively cooled.

The present invention also relates to a saddle-type vehicle equipped with the above-mentioned internal combustion engine. Preferably, in this saddle-type vehicle, the exhaust pipe is disposed below the engine body in the vertical direction of the vehicle or in front of the engine body in the longitudinal direction of the vehicle, and at least a part of the EGR passage portion is located on the opposite side of the engine body with the exhaust passage portion in between. With this configuration, it becomes possible to more actively blow the wind generated by the vehicle on the EGR passage portion of the exhaust pipe, thereby facilitating the cooling of the exhaust gas, i.e., the EGR gas, flowing through the EGR passage portion.

According to the above aspect of the present invention, the above configuration contributes to making the EGR system more compact, and therefore contributes to the installation of the EGR system in a saddle-type vehicle.

1 is an overall right side view of a motorcycle according to a first embodiment of the present invention. FIG. FIG. 2 is an enlarged right side view of a portion of the vehicle of FIG. 1 . FIG. 2 is a side view of a power unit, an intake system device, and an exhaust system of the motorcycle of FIG. 1 . FIG. 4 is a plan view of a portion of FIG. 3 . FIG. 2 is a bottom view of a portion of the motorcycle. FIG. 2 is a partial cross-sectional view taken along the crankshaft of the internal combustion engine of the power unit. FIG. 2 is an overall left side view of the motorcycle of FIG. 1 . 2 is a perspective view of an engine body and a part of an exhaust system of the internal combustion engine of the motorcycle of FIG. 1 . 2 is a perspective view of an engine body and a part of an exhaust system of the internal combustion engine of the motorcycle of FIG. 1, seen from another angle. FIG. 2 is an enlarged view of the connection of the exhaust system to the cylinder head of the internal combustion engine of the motorcycle of FIG. 1; FIG. FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. 1, (b) shows a modified example thereof, and (c) shows yet another modified example. FIG. FIG. 11 is an overall left side view of a motorcycle according to a second embodiment of the present invention. FIG. 16 is a front view of a portion of the motorcycle of FIG. 15 . FIG. 16 is a perspective view of a portion of the internal combustion engine of the motorcycle of FIG. 15 . FIG. 11 is a perspective view of a portion of a modified internal combustion engine. FIG. 11 is a schematic cross-sectional view of an exhaust pipe according to a modified example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described. A side view of a scooter-type motorcycle 1 according to this embodiment is shown in FIG.
In the explanations of this specification, the directions of front, back, left, right, and up and down follow the usual standard of the direction in which the motorcycle 1 of this embodiment moves straight ahead being the forward direction, and in the drawings, FR indicates the forward direction, RE indicates the rear, LH indicates the left, RH indicates the right, UP indicates the top, and DW indicates the bottom.

As shown in FIG. 1, a front body 1F and a rear body 1R are connected via a low floor portion 1C. A body frame F forming the skeleton of the vehicle body is generally composed of a down tube 3 and a main pipe 4.
That is, a down tube 3 extends downward from a head pipe 2 at the front part 1F of the vehicle body, bends horizontally at its lower end and extends rearward below the floor part 1C, and a pair of left and right main pipes 4 are connected to its rear end. The main pipes 4 form an inclined portion 4a that extends diagonally upward and rearward from the connected part, and the upper part of the inclined portion 4a is further bent to form a horizontal portion 4b that extends approximately horizontally rearward.

At the front body 1F, the head pipe 2 and the vertically oriented parts of the down tube 3 are covered from the front and rear by the front cover 1a and leg shield 1b, at the floor part 1C, the vertically oriented parts of the down tube 3 are covered by the lower side cover 1c, and at the rear body 1R, the main pipe 4 is covered on the left, right and rear sides by the body cover 1d. The lower side cover 1c, which covers the underside of the vehicle, extends from the lower part of the front cover 1a to the rear of the vehicle as shown in Figures 2 and 7, and covers part of the right side of the power unit P.

A storage box 5 and a fuel tank (not shown) are supported at the front and rear between the pair of main pipes 4, and a seat 7 is disposed to cover the storage box 5 and the fuel tank.
At the front portion 1F of the vehicle body, a handlebar 8 is provided above and journalled on the head pipe 2, and a front fork 9 extends below and has a front wheel 10 journalled at its lower end.

As shown in FIG. 1, a support bracket 11 protrudes rearward, located approximately halfway along the longitudinal direction of the inclined portion 4a of the main pipe 4. As shown in FIG. 2, a hanger 22h protrudes diagonally upward from the top of the power unit P. The support bracket 11 of the main pipe 4 and the hanger 22h are connected via a link member 12, and these link mechanisms connect and support the power unit P to the main pipe 4 so that it can swing.

Referring to FIG. 3, the power unit P has a single-cylinder, four-stroke, air-cooled internal combustion engine 20 at the front, which is mounted on a crankcase 22 that supports a crankshaft 21 oriented in the vehicle width direction, and a cylinder block 23, cylinder head 24, and head cover 25 that are stacked in sequence from the crankcase 22, which protrudes forward in a position that is tilted forward to a nearly horizontal position. Note that the part including the crankcase 22, cylinder block 23, cylinder head 24, and head cover 25 is referred to as the engine body B.

Referring to FIG. 6, the crankcase 22 is split into a left crankcase portion 22L and a right crankcase portion 22R, and the crankshaft 21, which is oriented in the vehicle width direction, is rotatably supported by the left crankcase portion 22L and the right crankcase portion 22R via main bearings 21b, 21b, respectively.

An AC generator 55 is provided on the right side of the crankshaft 21, and a centrifugal cooling fan 56 is attached integrally to an outer rotor 55r of the AC generator 55.
A fan cover 57 that covers the right crankcase portion 22R from the right side houses the centrifugal cooling fan 56. Referring also to Figure 2, the fan cover 57 is formed with a grill 57g that serves as an outside air inlet facing the centrifugal cooling fan 56. In this way, the centrifugal cooling fan 56 is an air-cooled fan.

As shown in Figure 6, the left crankcase 22L extends rearward and doubles as the transmission case, and the transmission case (left crankcase) 22L is covered from the left side by a transmission case cover 65, with the belt-type continuously variable transmission 60 disposed inside. A drive chain sprocket 58 is provided adjacent to the main bearing 21b on the left shaft portion of the crankshaft 21, and a drive pulley 61 of the belt-type continuously variable transmission 60 is provided on the left shaft end.

Power is transmitted to the valve mechanism on the cylinder head 24 side by a cam chain 59 that is wound around a drive chain sprocket 58 .
1 and 3, the reduction gear output shaft of the reduction mechanism 64 provided at the rear of the belt-type continuously variable transmission 60 is the rear axle 28a, and the rear wheel 28 is provided on the rear axle 28a.
A rear cushion (not shown) is interposed between the upper end of the rear part of the transmission case portion 22L, which houses the reduction gear mechanism 64, and the upper bent portion of the main pipe 4.

As shown in FIG. 3, the driven pulley 63 of the belt-type continuously variable transmission 60 is journaled on the reducer input shaft 64a of the reduction mechanism 64, and a belt 62 is wound around the drive pulley 61 provided on the crankshaft 21 and the driven pulley 63 provided on the reducer input shaft 64a, so that the power of the internal combustion engine 20 is transmitted to the driven pulley 63 via the belt 62, and the rotation of the driven pulley 63 is transmitted to the reducer input shaft 64a of the reduction mechanism 64 via a centrifugal clutch (not shown), and is reduced in speed by the reduction mechanism 64 before being transmitted to the rear wheel 28. As shown in FIG. 6, an outside air intake fan 61F is formed on the left pulley half of the drive pulley 61.

The cylinder block 23 and cylinder head 24 are surrounded by a shroud 70, which is an air guide member as shown in FIG. 6, and the shroud 70 is connected to the fan cover 57 on the right side. Therefore, air can be blown through the shroud 70 to each part of the cylinder block 23 and cylinder head 24, for example, around the outlet of the exhaust port 24b of the cylinder head 24 of the internal combustion engine 20.

3, an intake port 24a is formed on the upper surface of a cylinder head 24 of the internal combustion engine 20 in the front part of the power unit P, and an inlet pipe 31 serving as an intake pipe extends upward from the intake port 24a. An exhaust port 24b is formed on the lower surface of the cylinder head 24, and an exhaust pipe 51 extends downward from the exhaust port 24b.
An ignition plug 26 is inserted into the cylinder head 24 near the center of the head cover 25, and an oxygen concentration sensor 27 is inserted into the cylinder head 24 at the location where the exhaust passage E extends.

An intake device 30 that draws in outside air and sends it to the internal combustion engine 20 is connected to the intake port 24a of the internal combustion engine 20. The inside of the intake device 30 forms an intake passage through which the intake air sent to the internal combustion engine 20 passes, which introduces the intake air into the combustion chamber 20a of the internal combustion engine 20.
The intake device 30 comprises an air cleaner device 40 that takes in and purifies outside air, a connecting tube 36 connected to the air cleaner device 40, a throttle body 33 connected to the downstream side of the connecting tube 36, and an inlet pipe 31 connected to the upstream side of the throttle body 33, and these together form the intake system.

As shown in Figure 4, the air cleaner device 40 of the intake system 30 has an air cleaner case 41 which combines left and right unpurified chamber cases 42 and purified chamber cases 43, and is divided into an unpurified chamber Ca on the unpurified chamber case 42 side and a purified chamber Cb on the purified chamber case 43 side by a partition disposed between the unpurified chamber case 42 and the purified chamber case 43 and in which an air cleaner element 44 is disposed.
As shown in Figure 3, an air intake pipe 47 for taking in airflow from running is disposed in the unpurified chamber case 42 with its opening 47a facing forward. The intake air introduced from the opening 47a passes through the unpurified chamber Ca and the air cleaner element 44, where it is purified, and sent to the purified chamber Cb. The purified chamber Cb of the air cleaner device 40 is connected to the throttle body 33 by a rubber connecting tube 36 which is elastically deformable. A fuel injection valve 37 is attached to the upper surface of each of the throttle body 33 and the inlet pipe 31, and injects fuel into the intake passage.

5, an exhaust device 50 is connected to the exhaust port 24b of the cylinder head 24. The exhaust device 50 includes an exhaust pipe 51 connected to the exhaust port 24b, a muffler 52 connected to the rear end of the exhaust pipe 51 and with an atmosphere opening port 52a facing toward the rear of the vehicle, and a catalytic converter 53 built into the exhaust pipe 51.
Exhaust gas discharged from the internal combustion engine 20 flows into an exhaust pipe 51 from the exhaust port 24b, is purified by a catalytic device 53 provided midway through the exhaust pipe 51, passes through a muffler 52, and is discharged into the atmosphere from an air opening 52a.

The exhaust pipe 51 communicates with the exhaust port 24b, extends downward from the underside of the cylinder head 24, bends diagonally forward to the left, then bends from the rear to the right, bends from the left to the right of the lower part of the crankcase 22, extends rearward, and is connected to a muffler 52 disposed on the right side of the rear wheel 28.

The exhaust pipe 51 is composed of a catalytic converter-containing exhaust pipe 51c in which a catalytic converter 53 is built, an upstream exhaust pipe 51a connected to the upstream side of the catalytic converter-containing exhaust pipe 51c, and a downstream exhaust pipe 51b connected to the downstream side of the catalytic converter-containing exhaust pipe 51c.

The upstream exhaust pipe 51a is connected to the exhaust port 24b and extends downward from the underside of the cylinder head 24 (see also Figure 3), then bends diagonally forward on the left side and then bends again from the rear to the right to connect to the catalytic converter-containing exhaust pipe 51c.

The catalytic converter-accommodating exhaust pipe 51c is located below the internal combustion engine 20 and is arranged so that the exhaust gas flows in the vehicle width direction from the left side to the right side of the vehicle.
The catalytic converter-accommodating exhaust pipe 51c is disposed so that its upstream end is located on the left side in the vehicle width direction and its downstream end is located on the right side in the vehicle width direction. The upstream end is connected to the upstream exhaust pipe 51a, and the downstream end is connected to the downstream exhaust pipe 51b.

The catalytic converter 53 is housed inside the catalytic converter-housed exhaust pipe 51c with its axis oriented in the vehicle width direction. The catalytic converter 53 is a honeycomb-shaped porous structure with numerous pores extending in the axial direction, and the porous structure supports a catalyst such as platinum, rhodium, or palladium as a component that breaks down exhaust gas. Here, the catalytic converter 53 may be simply referred to as a catalyst.

As shown in FIG. 5, the downstream exhaust pipe 51b is connected to the downstream side of the catalytic converter housing exhaust pipe 51c, extends in the vehicle width direction, and then curves toward the rear. In a bottom view of the vehicle, the downstream exhaust pipe 51b extends rearward along the vehicle front-rear direction on the outer side in the vehicle width direction from the crankcase 22 that constitutes the unit case Pc. Furthermore, as shown in FIG. 2 and FIG. 7, in a right side view of the vehicle body, the downstream exhaust pipe 51b extends rearward from the right side of the lower part of the power unit P, then bends and extends diagonally upward, and is connected to a muffler 52 disposed on the right side of the rear wheel 28.

2 is a right side view of the vicinity of the power unit P with a portion of the front side of the fan cover 57 cut away. In this side view, the downstream exhaust pipe 51b has two curved portions 51d, one on the upstream side and _one on the downstream side. The downstream exhaust pipe 51b is formed so that, of these curved portions 51d, the upstream curved portion 51d1 closest to the catalytic converter-accommodated exhaust pipe 51c is located forward of the rotation center C1 of the cooling fan in the vehicle front-rear direction in the vehicle side view.
The saddle-type vehicle of this embodiment has two curved portions 51d, but it is sufficient to have at least one curved portion 51d, and may have two or more curved portions 51d.

An exhaust gas sensor 54 is attached to the downstream exhaust pipe 51b and detects the oxygen concentration in the exhaust gas that has passed through the catalytic device 53. The exhaust gas sensor 54 may be either an LAF sensor or an _O2 sensor.

2 and 6, a fan cover 57 constituting a part of the unit case Pc is disposed near the downstream exhaust pipe 51b and the exhaust gas sensor 54, covering the right side of the centrifugal cooling fan 56. The fan cover 57 is integrally connected to a shroud 70 that covers a part of the internal combustion engine 20, and covers the right side of the internal combustion engine 20. The eaves portion 57d of the fan cover 57 is formed to cover the right side of the downstream exhaust pipe 51b. The edge of the eaves portion 57d of the fan cover 57 is formed with a cutout portion 57e that opens forward in the vehicle front-rear direction. The cutout portion 57e is formed to avoid the exhaust gas sensor 54 attached to the downstream exhaust pipe 51b, and as shown in FIG. 2, the cutout portion 57e and the exhaust gas sensor 54 overlap in a side view of the vehicle.

The motorcycle 1 is equipped with an ECU (electronic control unit) (not shown). The ECU controls the internal combustion engine 20 and other components. The ECU is configured as a computer, and includes a processor (e.g., a CPU) and memory (e.g., a ROM and a RAM), and receives output signals from various sensors. For example, an engine speed sensor, an engine load sensor such as a throttle opening sensor, an oxygen concentration sensor 27, and an exhaust gas sensor 54 are connected to the ECU. The ECU analyzes the operating state based on the inputs from these sensors, and controls the operation of the spark plug 26, the fuel injection valve 37, the throttle valve of the throttle body 33, the EGR valve V (described later), and other components based on the analyzed operating state.

Now, the exhaust device 50 of the internal combustion engine 20 will be further explained. Figs. 8 and 9 show perspective views of a part of the engine body B and the part up to the catalytic converter-accommodated exhaust pipe 51c that defines the exhaust passage E. Fig. 8 is a perspective view of the cylinder head 24 side of the engine body B as seen from the diagonally right front side of the vehicle, and Fig. 9 is a perspective view of the cylinder head 24 side of the engine body B as seen from the diagonally left rear side of the vehicle. Fig. 10 is an enlarged view of the connection part of the exhaust device 50 to the exhaust port 24b of the cylinder head 24. Figs. 11 to 13 show the upstream exhaust pipe 51a and the catalytic converter-accommodated exhaust pipe 51c of the exhaust pipe 51. Fig. 11 is a perspective view of a cross section along the exhaust flow direction of the catalytic converter-accommodated exhaust pipe 51c, and Fig. 12 is a cross section along the exhaust flow direction of the catalytic converter-accommodated exhaust pipe 51c, in which the exhaust flow direction, i.e., the axis 51ca of the catalytic converter-accommodated exhaust pipe 51c, is arranged parallel to the paper surface. FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. 12, which is a plane perpendicular to the exhaust flow direction of the catalytic converter-accommodated exhaust pipe 51c, and is a cross-sectional view in which the exhaust flow direction, i.e., the axis 51ca of the catalytic converter-accommodated exhaust pipe 51c, is positioned perpendicular to the paper surface.

The internal combustion engine 20 is equipped with an EGR system S to perform EGR, particularly external EGR, which recirculates exhaust gas from the exhaust system to the intake system. The EGR system S includes an EGR passage Ep. Furthermore, the EGR system S includes an EGR valve V. Here, the EGR valve V is attached directly to the cylinder head 24 so as to guide the exhaust gas recirculated to the intake port 24a, i.e., the EGR gas, but it may be provided at any position in the EGR passage Ep so as to guide the exhaust gas to an intake pipe such as an inlet pipe 31. Note that the EGR valve V is a poppet type valve here, but may be another type of valve.

The EGR passage portion 68a, which is a part of the EGR passage Ep, is formed in the catalytic converter housing exhaust pipe 51c. The catalytic converter housing exhaust pipe 51c has a double pipe structure as shown in Figures 11 to 13. The catalytic converter housing exhaust pipe 51c has an inner pipe portion 66, the axis 51ca of the catalytic converter housing exhaust pipe 51c extending therein as its axis, and an outer pipe portion 68 outside the inner pipe portion 66. The inner pipe portion 66 has a substantially cylindrical passage, and defines an exhaust passage portion 66a through which exhaust gas discharged from the exhaust port 24b to the exhaust passage E flows toward the muffler 52. The outer pipe portion 68 extends adjacent to and in contact with the periphery of the inner pipe portion 66, and extends along the axis 51ca of the catalytic converter housing exhaust pipe 51c as its axis, defining a cylindrical space. The cylindrical space of the outer pipe portion 68 becomes an EGR passage portion 68a through which the recirculated exhaust gas, i.e., EGR gas, flows. The inner pipe portion 66 and the outer pipe portion 68 are integrated by a cylindrical partition wall 71. That is, the catalytic converter-accommodated exhaust pipe 51c has a partition wall 71 that divides its interior into an exhaust passage portion 66a and an EGR passage portion 68a, and the EGR passage portion 68a is adjacent to the exhaust passage portion 66a within the catalytic converter-accommodated exhaust pipe 51c via the partition wall 71. In particular, since the catalytic converter-accommodated exhaust pipe 51c has a double pipe structure, the EGR passage portion 68a is partitioned and formed by the partition wall 71 on the outside of the exhaust passage portion 66a within the catalytic converter-accommodated exhaust pipe 51c. The partition wall 71 is a cylindrical pipe section whose axis is the axis 51ca of the catalytic converter-accommodating exhaust pipe 51c, so that the longitudinal directions of the exhaust passage section 66a and the EGR passage section 68a are roughly aligned and in a roughly parallel relationship.

The aforementioned catalytic device 53, which is equipped with a catalyst, is disposed in the exhaust passage portion 66a of the catalytic device-accommodating exhaust pipe 51c. A communication passage 72 that connects the exhaust passage portion 66a and the EGR passage portion 68a is defined downstream of the catalytic device 53 in the exhaust passage portion 66a. The communication passage 72 is formed at the downstream end of the catalytic device-accommodating exhaust pipe 51c, and is defined by a notch 74 formed at the downstream end of the partition wall 71. The communication passage 72 is a hole that extends radially around the axis 51ca of the catalytic device-accommodating exhaust pipe 51c, and allows a portion of the exhaust gas in the exhaust passage portion 66a to be drawn into the EGR passage portion 68a by the negative pressure of the intake system.

A gas discharge section 76 is formed at the upstream end of the catalytic converter-accommodating exhaust pipe 51c. The gas discharge section 76 enables exhaust gas in the EGR passage section 68a to be discharged from the EGR passage section 68a. The gas discharge section 76 defines a gas discharge path 76a that communicates with the EGR passage section 68a. Therefore, in the catalytic converter-accommodating exhaust pipe 51c, the exhaust gas recirculated in the EGR passage section 68a, i.e., the EGR gas, flows in the opposite direction to the flow direction of the exhaust gas toward the downstream side in the exhaust passage section 66a.

An EGR pipe 78 is connected to the gas discharge section 76. The EGR pipe 78 is an example of an EGR pipe section, and defines an EGR passage section (hereinafter, a second EGR passage section) 78a connected to the EGR passage section 68a of the exhaust pipe 51c housing the catalytic converter. The EGR pipe 78 is arranged to extend toward the engine body B. Here, as shown in Figures 5, 8 and 10, the EGR pipe 78 is directly connected to the cylinder head 24 of the engine body B, and enables EGR gas to be guided to the EGR passage section 24e defined in the engine body B. As shown in Figures 2, 5, 8 to 10 and 12, the EGR pipe 78 is arranged to extend generally within the area surrounded by the upstream exhaust pipe 51a and the exhaust pipe 51c housing the catalytic converter, and extends downward from the connection section of the exhaust pipe 51c housing the catalytic converter, then faces upward and connects to the underside of the cylinder head 24. Therefore, the EGR pipe 78 is a generally U-shaped pipe. Note that the EGR passage portion 24e may be formed in a location other than the cylinder head 24 in the engine body B.

Figure 14(a) shows a schematic diagram of the EGR system S. Figure 14(a) shows the EGR system S of this embodiment. In the EGR system S, the exhaust gas discharged from the engine body B flows in order through the exhaust port 24b and the upstream exhaust pipe 51a, passes through the catalytic device 53 in the exhaust passage portion 66a of the catalytic device-accommodating exhaust pipe 51c, and when the EGR valve V is controlled to be opened by the above-mentioned ECU (not shown), flows through the communication passage 72 to the EGR passage portion 68a, flows out from the gas discharge portion 76 to the outside of the catalytic device-accommodating exhaust pipe 51c, flows through the second EGR passage portion 78a of the EGR pipe 78 to the EGR passage portion 24e of the engine body B, and is returned to the intake passage, here the intake port 24a, through the EGR valve V. As a result, the returned exhaust gas, i.e., the EGR gas, is sucked into the combustion chamber 20a.

When exhaust gas is recirculated in this manner, a cooling means is provided midway through the EGR passage Ep. First, the EGR pipe 78, which is the EGR pipe section, is provided with a heat dissipation section 80. The heat dissipation section 80 is configured to increase the surface area of the EGR pipe 78 exposed to the outside air, and is a pleated, or bellows-shaped pipe section. The EGR pipe 78 is exposed to the outside below the vehicle body where the wind flows, and is provided with the heat dissipation section 80, so it can provide a high cooling effect.

Furthermore, as described above, the shroud 70, which is an air guide member provided to surround the cylinder block 23 and the cylinder head 24, is connected to the fan cover 57 of the air-cooled fan, i.e., the centrifugal cooling fan 56, provided on one end side of the crankshaft 21 of the internal combustion engine. One edge 70a of the shroud 70 opens around the outlet of the exhaust port 24b of the cylinder head 24 of the internal combustion engine 20 as shown in FIG. 10, making it possible to send the wind of the centrifugal cooling fan 56 to the exhaust port 24b, i.e., the upstream exhaust pipe 51a side that communicates with it. Here, as shown in FIG. 5, FIG. 8 and FIG. 10, the EGR pipe 78 is arranged next to the upstream exhaust pipe 51a, i.e., the exhaust port 24b that it communicates with, in terms of the connection position on the exhaust port 24b side of the cylinder head 24. And, the position of the connection position of the EGR pipe 78 to the cylinder head 24 is located in the path of the wind of the centrifugal cooling fan 56 flowing out from the shroud 70. Therefore, the EGR pipe 78 can receive the wind from the centrifugal cooling fan 56 that is discharged from one edge 70a of the shroud 70. In FIG. 10, the wind from the centrifugal cooling fan 56 flowing toward the EGR pipe 78 is shown diagrammatically by arrow A1.

The following describes the characteristic configurations of the exhaust device 50 of the internal combustion engine 20 and the associated effects in the motorcycle 1, which is a saddle-type vehicle with the above configuration.

In the exhaust device 50 of the internal combustion engine 20 mounted on the motorcycle 1, the catalytic converter-accommodating exhaust pipe 51c includes an exhaust passage portion 66a through which exhaust gas discharged from the combustion chamber 20a flows, and an EGR passage portion 68a. The catalytic converter-accommodating exhaust pipe 51c has a partition wall 71 that separates the exhaust passage portion 66a and the EGR passage portion 68a. Therefore, the EGR passage portion 68a can be arranged adjacent to the exhaust passage portion 66a, and the exhaust passage portion 66a and the EGR passage portion 68a can be integrated into one exhaust pipe 51c, thereby reducing the dead space between the exhaust passage portion 66a and the EGR passage portion 68a and contributing to the compactness of the EGR system S. Therefore, the exhaust device 50 can contribute to the mounting of the EGR system S on the motorcycle 1, which is a saddle-type vehicle. In addition, the catalytic converter-accommodated exhaust pipe 51c has a partition wall 71 separating the exhaust passage portion 66a and the EGR passage portion 68a, and thus the EGR passage portion 68a can be arranged adjacent to the exhaust passage portion 66a in the catalytic converter-accommodated exhaust pipe 51c. Therefore, compared with the case where the catalytic converter-accommodated exhaust pipe forming the exhaust passage portion 66a and the EGR pipe forming the EGR passage portion 68a are provided, the appearance of the catalytic converter-accommodated exhaust pipe 51c can be made closer to or substantially the same as the appearance of a conventional circular exhaust pipe. In particular, the exhaust passage portion 66a and the EGR passage portion 68a are formed in the exhaust pipe 51c in a substantially parallel relationship, so that the EGR passage portion 68a can be more integrally integrated with the exhaust pipe 51c. Furthermore, the exhaust pipe 51c is provided with the above-mentioned communication passage 72, which is a communication portion, so that the EGR passage portion 68a can be more integrally integrated with the exhaust pipe 51c. Thus, the exhaust system 50 is significantly different from conventional exhaust systems in that it has an exhaust pipe 51c that has a configuration that combines an EGR passage section 68a with a normal exhaust passage section 66a, in addition to the exhaust pipe 51c that has a configuration that combines an EGR passage section 68a.

The partition wall 71 is provided in the catalytic converter-accommodating exhaust pipe 51c so as to define the EGR passage portion 68a outside the exhaust passage portion 66a. Here, the partition wall 71 is provided inside the exhaust pipe 51c so that the exhaust pipe 51c has a double pipe structure. Therefore, the EGR passage portion 68a adjacent to the exhaust passage portion 66a can be effectively formed on the outside while ensuring a sufficient cross-sectional area of the exhaust passage portion 66a, in other words, without impairing it. In addition, the exhaust pipe 51c with a double pipe structure can be manufactured at a relatively low cost, so this configuration is also excellent in terms of cost. Furthermore, since the exhaust pipe 51c has a double pipe structure and the EGR passage portion 68a is formed therein, the EGR passage portion 68a cannot be seen from the outside, and the additional formation of the EGR passage portion 68a can be further prevented from impairing the appearance of the exhaust pipe 51c.

Furthermore, the catalytic converter-accommodating exhaust pipe 51c is provided with a catalyst, i.e., catalytic converter 53, in the exhaust passage portion 66a. Therefore, the catalyst can be warmed up by the exhaust gas flowing through the EGR passage portion 68a. In addition, the catalytic converter-accommodating exhaust pipe 51c is provided with the above-mentioned communication passage 72 so that the exhaust gas downstream of the catalytic converter 53 can flow to the EGR passage portion 68a, so that the exhaust gas purified by the catalytic converter 53 can flow into the intake system of the internal combustion engine. Furthermore, because the catalytic converter-accommodating exhaust pipe 51c is configured with the above-mentioned communication passage 72, the configuration of the EGR passage Ep can be simplified, and the EGR system S can be made even more compact.

The EGR pipe 78 that defines the second EGR passage portion 78a extends toward the engine body B. This makes it possible to compactly arrange the second EGR passage portion 78a, i.e., the EGR pipe 78, around the engine body B in each of the motorcycle 1 and the internal combustion engine 20, thereby contributing to a more compact EGR system S.

The EGR pipe 78 is also directly connected to the cylinder head 24 of the engine body B, and defines an EGR passage portion 24e, which is part of the EGR passage Ep, inside the engine body B. This makes it possible to further compact the EGR system S.

Furthermore, the EGR pipe 78 is provided with a heat dissipation section 80. This allows the exhaust gas flowing through the EGR pipe 78, i.e., the EGR gas, to be cooled more effectively. However, this does not exclude the provision of an additional EGR cooler before, after, or during the EGR pipe 78, and an additional EGR cooler may be provided.

The internal combustion engine 20 also includes a centrifugal cooling fan 56 provided on one end of the crankshaft 21, and a shroud 70, which is an air guide member that guides the wind from the centrifugal cooling fan 56 to the exhaust port 24b of the engine body B. The EGR pipe 78 is arranged next to the exhaust port 24b of the engine body B so that it can receive the wind discharged from the shroud 70. This allows the wind from the centrifugal cooling fan 56 to more effectively cool the EGR pipe 78, i.e., the exhaust gas flowing inside it.

The catalytic converter-accommodating exhaust pipe 51c is disposed below the engine body B in the vertical direction of the motorcycle 1. This results in the catalytic converter-accommodating exhaust pipe 51c being exposed below the motorcycle 1. Furthermore, as is clear from the fact that the catalytic converter-accommodating exhaust pipe 51c has a double-pipe structure, at least a portion of the EGR passage portion 68a is located on the opposite side of the engine body B across the exhaust passage portion 66a. This makes it possible to more actively direct the wind from traveling at the catalytic converter-accommodating exhaust pipe 51c including the EGR passage portion 68a, thereby facilitating the cooling of the exhaust gas, i.e., the EGR gas, flowing through the EGR passage portion 68a.

In the internal combustion engine 20 of the motorcycle 1, the EGR passage portion 24e connected to the second EGR passage portion 78a of the EGR pipe 78 is formed in the engine body B. However, the EGR pipe 78 may be connected to an intake pipe, such as the inlet pipe 31, without the EGR passage portion 24e formed in the engine body B. FIG. 14(b) shows an EGR system Sa in which the EGR pipe 78 is directly connected to the EGR valve V. In this configuration of the EGR system Sa, the EGR pipe 78 passes around the engine body E and is connected to the inlet pipe 31, which is an intake pipe, via the EGR valve V. This allows the EGR passage Ep to be arranged compactly. In FIG. 14(b), the EGR valve V is attached to the engine body B, but it may be provided away from the engine body B to connect the EGR pipe 78 to an intake pipe such as the inlet pipe 31.

Alternatively, as in the EGR system Sb shown in FIG. 14(c), an EGR passage portion 82 may be defined in the upstream exhaust pipe 51a. In this case, the EGR pipe 78 is connected to the upstream exhaust pipe 51a, and the second EGR passage portion 78a of the EGR pipe 78 is connected to the EGR passage portion 82 of the upstream exhaust pipe 51a. In this case, the EGR passage portion 82 may be connected to the EGR passage portion 24e of the engine body B via the EGR passage portion 84a of a further EGR pipe 84 as shown in FIG. 14(c), or may be connected to the intake pipe via the EGR valve V without passing through the EGR passage portion 24e of the engine body B as shown in FIG. 14(b).

Next, a second embodiment of the present invention will be described. Figure 15 shows a left side view of a motorcycle 101 according to the second embodiment, and Figure 16 shows a front view of a portion of the motorcycle 101.

The motorcycle 101 is equipped with a body frame 102 on which a power unit P and electrical equipment are mounted. The main tube of the body frame 102 extends rearward from a head pipe 103 located at the front end. The down tube 104 of the body frame 102 is provided so as to extend diagonally downward and rearward from the head pipe 103. A fuel tank 105 that contains fuel is disposed behind the head pipe 103. A seat 106 on which the rider sits is mounted behind this fuel tank 105. A footrest 107 on which the rider rests his/her feet while riding is provided below the seat 106.

A brake pedal 108 for the rear wheel WR, which is a drive wheel, is provided near the footrest 107 on the right side of the vehicle body shown in Fig. 15. The brake pedal 108 is pivoted at its rear end 108r located behind the footrest 107, and its front end 108f located in front of the footrest 107 is provided so as to be able to swing up and down. In a side view of the motorcycle 101 in Fig. 15, the brake pedal 108 is initially slightly inclined downward toward the front as it moves from the rear end 108r to the front end 108f, then becomes roughly horizontal, and then is further slightly inclined upward toward the front, forming a roughly U-shape. In other words, the brake pedal 108 extends in the front-rear direction without being inclined in the up-down direction in a side view of the motorcycle 101. The front end 108f of the brake pedal 108 functions as a pedal section, is located to the right of the front end portion of the crankcase 109 (described later), and is located at approximately the same height as the footrest 107, and can be depressed by the driver's foot placed on the footrest 107.

Furthermore, near the footrest 107 on the right side of the vehicle body shown in FIG. 15, a kick pedal 110 is provided, particularly above the footrest 107. The kick pedal 110 has a rear end 110r positioned diagonally above and rearward of the footrest 107, and a front end 110f positioned near the rear of the cylinder head 112 of the engine body B of the internal combustion engine 111 of the power unit P. As the kick pedal 110 moves from the rear end 110r to the front end 110f, it first extends upward and then curves forward. When in use, the kick pedal 110 is deployed so as to extend outward in the vehicle width direction. The front end 110f of the kick pedal 110 functions as a pedal portion and is depressed by the driver's foot. This depression causes the kick pedal 110 to rotate within a predetermined range around the rear end 110r, thereby starting the internal combustion engine 111.

The engine body B of the internal combustion engine 111 is suspended on the main tube and down tube 104 of the vehicle body frame 102. The engine body B includes a crankcase 109 supported on the down tube 104 via a bracket, and a cylinder block 113, a cylinder head 112, and a head cover 114, which are provided above the crankcase 109 in this order. The cylinder block 113 is connected to the top of the crankcase 109 in a forward-tilted state. Therefore, as shown in FIG. 15, the cylinder axis 111c of the cylinder of the engine body B is inclined obliquely forward from the crankshaft side of the crankcase 109 toward the cylinder head 112 side. The crankshaft extends in the vehicle width direction and is roughly perpendicular to the up-down direction and the front-rear direction. In FIG. 15, the rotation axis 115 of the crankshaft is shown.

The upper end (upstream end) of the upstream exhaust pipe 117 of the exhaust device 116 is connected to the cylinder head 112 of the engine body B. Exhaust gas discharged from the combustion chamber (not shown) flows through the upstream exhaust pipe 117 via the exhaust port of the cylinder head 112 and is discharged from the muffler 118 located to the right of the rear wheel WR, that is, located at the rear right side of the vehicle body. The exhaust port of the cylinder head 112, the upstream exhaust pipe 117, the catalytic converter housing exhaust pipe 120, the downstream exhaust pipe 121, and the muffler 118 are connected in this order in the exhaust flow direction, and each defines a part of the exhaust passage 122.

A front fork 123 is rotatably supported at the front end of the main tube via a steering shaft attached to the head pipe 103. A handlebar 124 is attached to the upper end of the steering shaft, and grips 125 are attached to both ends of the handlebar 124. A front wheel WF is rotatably supported at the bottom of the front fork 123. The upper part of the front wheel WF is partially covered by a front fender 126.

A rear wheel WR, to which the power of the internal combustion engine 111 is transmitted via a swing arm, is rotatably supported behind the engine body B. A suspension 126 that absorbs shocks from the road surface is disposed between the swing arm and the vehicle body frame 102. A rear fender 127 is disposed above and behind the rear wheel WR and behind the seat 106.

Now, as mentioned above, the upstream exhaust pipe 117 of the exhaust system 116 is connected to the front wall of the cylinder head 112 of the engine body B, and downstream of it, the catalytic converter housing exhaust pipe 120, which is an exhaust purification device, the downstream exhaust pipe 121, and the muffler 118 are arranged in this order from the upstream side. The catalytic converter housing exhaust pipe 120 has the same configuration as the catalytic converter housing exhaust pipe 51c described above, so a detailed explanation will not be given here, but it has a double pipe structure, and as shown in FIG. 17, it has a partition wall 128, and inside it, it has an exhaust passage part 129 separated by the partition wall 128 and an EGR passage part 130 on the outside, and the exhaust passage part 129 has a catalytic converter 131. Note that FIG. 17 shows a part of the catalytic converter housing exhaust pipe 120 in perspective.

15 and 16, the exhaust passage 122 continuing from the exhaust port of the cylinder head 112 of the engine body B extends to the front side of the engine body B, then extends downward, and further extends rearward through the lower side of the engine body B. In other words, the exhaust device 116 extends downward from the front side of the engine body B of the internal combustion engine 111, and extends rearward through the lower side of the engine body B. The catalytic converter-accommodated exhaust pipe 120 is positioned in front of the engine body B in the vehicle front-rear direction, and is particularly positioned in front of the crankcase 109. Therefore, the catalytic converter-accommodated exhaust pipe 120 is positioned in front of the vehicle from the front end 108f of the brake pedal 108. Here, since the exhaust passage 122 extends around the engine body B as described above, the catalytic converter-accommodated exhaust pipe 120 is arranged to extend obliquely in the same manner as the cylinder axis 111c in a side view of the motorcycle 101, and to extend obliquely rearward and downward from the upstream side to the downstream side. As shown in a front view of a portion of motorcycle 101 in Figure 16, when a central imaginary plane IS (a line extending vertically at the front wheel WF) is defined that extends from the front to the rear of motorcycle 101, catalytic converter-accommodating exhaust pipe 120 is located on the right side of the plane, and here extends to the right of front wheel WF, and is provided on motorcycle 101 so that its downstream portion is slightly inside in the vehicle width direction compared to its upstream portion. The central imaginary plane IS can be defined so as to be perpendicular to the vehicle width direction and to substantially bisect the front wheel WF and rear wheel WR.

In the exhaust device 116 of the internal combustion engine 111 of the motorcycle 101, the catalytic converter housing exhaust pipe 120 has the same configuration as the catalytic converter housing exhaust pipe 51c described above, so that the EGR pipe 132, which is an EGR pipe section, is connected to the catalytic converter housing exhaust pipe 120 so as to guide the exhaust gas flowing through the EGR passage portion 130 of the catalytic converter housing exhaust pipe 120 to the outside. Also, as in the first embodiment, the EGR pipe 132 is directly connected to the engine body B, and therefore the second EGR passage portion 132a of the EGR pipe 132 is connected to an EGR passage portion (not shown) of the engine body B. In this way, the EGR system Sc mounted on the internal combustion engine 111 of the motorcycle 101 has the same configuration as the EGR system S (see FIG. 14(a)). The EGR valve in the EGR system Sc is not shown. The EGR pipe 132 has the same heat dissipation portion 133 (see FIG. 17) as the heat dissipation portion 80.

Therefore, the motorcycle 101, the internal combustion engine 111 mounted thereon, and the exhaust system 116 thereof have the same configuration as those in the first embodiment described above, and similarly achieve the above-mentioned effects.

In addition, in the motorcycle 101 of this embodiment, the catalytic converter-accommodated exhaust pipe 120 is disposed in front of the engine body B in the longitudinal direction of the motorcycle 101. Since the catalytic converter-accommodated exhaust pipe 120 has a double-pipe structure, a part of the EGR passage portion 130 of the catalytic converter-accommodated exhaust pipe 120 is located on the opposite side of the engine body B across the exhaust passage portion 129. In other words, a part of the EGR passage portion 130 is located in front of the engine body B, and is located at the frontmost part of the catalytic converter-accommodated exhaust pipe 120. Therefore, it is possible to more actively apply the wind generated by running to the catalytic converter-accommodated exhaust pipe 120 including the EGR passage portion 130, thereby promoting the cooling of the exhaust gas flowing through the EGR passage portion 130, i.e., the EGR gas.

Furthermore, in the motorcycle 101, as shown in FIG. 16, part of the EGR pipe 132 is exposed to the right front side without being hidden by the front wheel WF depending on the angle of the front wheel WF. This can further promote cooling of the exhaust gas flowing through the EGR pipe 132. Therefore, the EGR system Sc can omit an EGR cooler. Note that the EGR system Sc may also be equipped with an EGR cooler.

The motorcycle 101, the internal combustion engine 111, and the exhaust system 116 can be modified to have the various configurations described as the modified examples of the first embodiment, specifically the configurations of FIG. 14(b) and FIG. 14(c). For example, as shown in FIG. 18, the upstream exhaust pipe 117a may have a double pipe structure and include an EGR passage portion 134. In this case, the EGR passage portion 130 of the catalytic converter-accommodating exhaust pipe 120 and the EGR passage portion 134 of the upstream exhaust pipe 117a are connected by an EGR pipe 135, and the EGR passage portion 134 of the upstream exhaust pipe 117a and an EGR passage portion (not shown) of the engine body B are connected by an EGR pipe 136. The EGR pipe 136 has a heat dissipation portion 137. The EGR pipe 135 can also have a heat dissipation portion.

Although the embodiments and their modifications according to the present invention have been described above, the present invention is not limited thereto. Various substitutions and modifications are possible without departing from the spirit and scope of the present invention as defined by the claims of this application.

For example, the catalytic converter-accommodating exhaust pipe 51c, 120 has a double pipe structure, and the EGR passage portion 68a, 130 is separated from the exhaust passage portion 66a, 129 by a cylindrical partition wall 71, 128, and extends cylindrically outside the exhaust passage portion 66a, 129. However, the catalytic converter-accommodating exhaust pipe is not limited to this configuration, and may have a partition wall of a shape other than a cylindrical shape. For example, the catalytic converter-accommodating exhaust pipe may have a flat partition wall inside, and the flat partition wall may divide the internal space into two spaces, one of which is the exhaust passage portion and the other is the EGR passage portion. Note that the exhaust pipe having an EGR passage portion and an exhaust passage portion is not limited to an exhaust pipe having a catalytic converter in its exhaust passage portion, and may also include an exhaust pipe not having a catalytic converter in its exhaust passage portion.

19 shows a catalytic converter-accommodated exhaust pipe 150, which is a modified example of the catalytic converter-accommodated exhaust pipes 51c and 120. FIG. 19 is a schematic cross-sectional view of the catalytic converter-accommodated exhaust pipe 150, cut downstream of the catalytic converter 152, i.e., the catalyst, which corresponds to the catalytic converters 53 and 131, and viewed from the cut surface to the upstream side. The catalytic converter-accommodated exhaust pipe 150 has a partition wall 158 therein to partition an exhaust passage portion 154 and an EGR passage portion 156. The partition wall 158 is flat and extends along the axis 150A of the exhaust pipe 150. The partition wall 158 is positioned off the axis 150A, and the exhaust passage portion 154 is wider than the EGR passage portion 156. Thus, the EGR passage portion 156 is substantially partitioned outside the exhaust passage portion 154. A communication portion 160 that connects the exhaust passage portion 154 and the EGR passage portion 156 is formed in the partition wall 158. In this way, the exhaust passage portion 154 and the EGR passage portion 156 can be integrated into the exhaust pipe 150 by forming the partition wall 158. This also allows the appearance of the exhaust pipe 150 to be similar to that of a conventional circular exhaust pipe. Note that in FIG. 19, the gas exhaust portion that defines the gas exhaust passage that communicates with the EGR passage portion 156, that is, the portion corresponding to the gas exhaust portion 76, is not shown.

In the above embodiment, the partition walls 71, 128, 158 in the exhaust pipes 51c, 120, 150 are made of one wall member, but they may be made of two or more wall members. For example, a pipe member that defines the exhaust passage portion and a pipe member that defines the EGR passage portion may be arranged adjacent to each other with their longitudinal directions aligned, and pressed against each other to form a generally tubular shape, or may be further joined by welding, for example, to form a substantially single exhaust pipe 51c, 120, 150. In this case, the partition walls 71, 128, 158 are made of a part of the pipe member that defines the exhaust passage portion and a part of the pipe member that defines the EGR passage portion.

1, 101...Motorcycles
20, 111…Internal combustion engine
50, 116…Exhaust system
51a, 117, 117a...Upstream exhaust pipe
51c, 120, 150... Catalytic device housing exhaust pipe
53, 131, 152...Catalyst
66a, 129, 154...Exhaust passage section
68a, 130, 156...EGR passage part
71, 128, 158…Bulkhead
80, 133...Heat dissipation section

Claims (9)

an exhaust passage portion (66a, 129, 154) through which exhaust gas discharged from a combustion chamber (20a) flows;
an exhaust pipe (51c, 120, 150) having an EGR passage portion (68a, 130, 156);
the exhaust pipe (51c, 120, 150) has a partition wall (71, 128, 158) that separates the exhaust passage portion (66a, 129, 154) from the EGR passage portion (68a, 130, 156);
An exhaust system (50, 116) for an internal combustion engine (20, 111). the partition wall (71, 128, 150) is provided in the exhaust pipe (51c, 120, 150) so as to define the EGR passage portion (68a, 130, 156) outside the exhaust passage portion (66a, 129, 154);
2. An exhaust system (50, 116) for an internal combustion engine (20, 111) according to claim 1 . the exhaust pipe (51c, 120, 150) is provided with a catalyst (53, 131, 152) in the exhaust passage portion (66a, 129);
An exhaust system (50, 116) for an internal combustion engine (20, 111) according to claim 1 or 2. An internal combustion engine (20, 111) comprising an exhaust system for an internal combustion engine according to claim 1,
the exhaust pipe (51c, 120) further includes an EGR pipe portion (78, 132) that defines a second EGR passage portion (78a, 132a) connected to the EGR passage portion (68a, 130) of the exhaust pipe (51c, 120) and extends toward an engine body (B);
An internal combustion engine (20, 111). The EGR pipe portion (78, 132) is connected to the engine body (B).
5. An internal combustion engine (20, 111) according to claim 4. The EGR pipe portion (78, 132) passes around the engine body (B) and is connected to the intake pipe (31).
5. An internal combustion engine according to claim 4. The EGR pipe section (78, 132) includes a heat dissipation section (80, 133).
5. An internal combustion engine (20, 111) according to claim 4. The internal combustion engine (20, 111) includes an air-cooling fan (56) provided at one end side of a crankshaft (21) and an air guide member (70) that guides air from the air-cooling fan (56) to an exhaust port (24b) of the engine body (B),
the EGR pipe portion (78, 132) is arranged next to the exhaust port (24b) of the engine body (B) so as to be able to receive the wind discharged from the air guide member (70);
5. An internal combustion engine (20) according to claim 4. A saddle-type vehicle (1, 101) equipped with an internal combustion engine (20, 111) according to claim 4,
the exhaust pipe (51c, 120) is disposed below the engine body (B) in the up-down direction of the vehicle (1) or in front of the engine body (B) in the front-rear direction of the vehicle (101);
At least a part of the EGR passage portion (68a, 130) is located on the opposite side of the engine body (B) with the exhaust passage portion (66a, 129) interposed therebetween.
A saddle-type vehicle (1, 101).

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